1. Field of the Invention
The present invention relates to a plasma processing apparatus and, more particularly, to a processing apparatus in which a plasma is generated by an electron cyclotron resonance caused by a microwave and a magnetic field and a semiconductor wafer is processed (e.g., etched) by using this generated plasma.
2. Description of the Related Art
In recent years, Since micropatterning of semiconductor devices has been rapidly developed, demands for micropatterning precision, low contamination, less damage, and selectivity in dry-etching techniques have become stricter.
A method of causing a microwave discharge using a resonance phenomenon between an electron cyclotron motion and a microwave in a magnetic field has been recently employed. According to this microwave discharge, since a plasma having a high density can be generated by a non-electrode discharge in a low pressure, a high-speed surface treatment can be performed, and wafers are free from contamination, thus providing industrial advantages.
An example of a conventional plasma processing apparatus of this type is described in Published Examined Japanese Patent Application No. 58-13626. In this disclosed apparatus, a microwave is supplied downward into a plasma generation chamber around which a magnetic field forming means is arranged. A plasma is then generated by an electron cyclotron resonance. Ions in this plasma are extracted by an ion extraction electrode into a processing chamber from the bottom portion of the plasma generation chamber and are radiated on the surface of a target object located inside the processing chamber.
Another example of an apparatus of this type is described in Published Unexamined Japanese Patent Application No. 59-202635. In this disclosed apparatus, a discharge tube constituting a plasma generation chamber has a structure tapered wider from a microwave supply direction to the direction of a target object, and at the same time has a magnetic gradient. Therefore, ions can be transported to the target body and plasma processing in a wide area can be performed.
In the former apparatus, i.e., the apparatus described in Published Examined Japanese Patent Application No. 59-13626, the processing chamber must be arranged independently of the plasma generation chamber, resulting in a bulky apparatus. In addition, since a high voltage of about 1,000 V is required as an ion extraction voltage, the ion energy is high, and the surface of the target object is greatly damaged.
In the latter apparatus, i.e., the apparatus described in Published Unexamined Japanese Patent Application No. 59-202635, since the magnetic gradient is present from the plasma generation region to the surface of the target object, the lines of magnetic force are inclined with respect to the surface of the target object, so that the ions are obliquely incident on the surface of the target object. Therefore, for example, perpendicular etching performance is degraded, and excellent micropatterning becomes difficult.
On the other hand, when a target object is placed in the plasma generation chamber and a magnetic field having a uniform strength is formed in the plasma generation chamber, the separate processing chamber need not be arranged, and ions can be perpendicularly incident on the surface of the target object. In this case, however, the energy (temperature) of the electrons generated by an electron cyclotron resonance phenomenon is extremely increased. In addition, since a probability of collision between electrons and ions is low at a low pressure, the surface of the target object are bombarded with electrons having a high energy to cause a charge-up phenomenon, thereby increasing the floating potential to, e.g., 100 eV. For this reason, when ions pass through an ion sheath, their energy is considerably increased, and the ions having the high energy strike the surface of the target object. In addition to the bombardment with electrons having a high energy, thermal, electrostatic damage to the surface of the target object is increased. The energy of the microwave is absorbed in the target object to undesirably heat the target object to a high temperature.